A tunnel boring machine (“TBM”) is a tunnel excavation apparatus for forming tunnels in a variety of soil and rock strata. A conventional TBM produces a smooth circular tunnel wall, with minimal collateral disturbance. As discussed in U.S. Pat. No. 8,172,334, to Lindbergh et al., which is hereby incorporated by reference in its entirety, a conventional TBM includes a rotatably driven cutterhead that supports a plurality of disc cutter assemblies. Typically, a cutterhead may have 20, 50, 100, or more disc cutter assemblies rotatably mounted to the cutterhead. The disc cutter assemblies are removable from the cutterhead so that the disc cutter assemblies may be replaced or maintained.
A breakthrough that made TBMs efficient and reliable was the introduction of the disc cutter assembly by James S. Robbins in the 1950s. Initially, Robbins' TBM used rigid spikes rotating in a circular motion, but the spikes would frequently break. See, for example, U.S. Pat. No. 2,811,341, to Robbins. Robbins found that rotatable disc cutter assemblies provided greater reliability in the field. See, for example, U.S. Pat. No. 2,550,202, to Robbins. It is believed that virtually all modern TBMs use rotatable disc cutter assemblies.
In operation, the TBM cutterhead is urged against a surface, for example a tunnel face, such that at least some of the disc cutter assemblies engage the tunnel face. For example, in some TBMs a plurality of hydraulic cylinders are configured to engage the tunnel walls aft of the cutterhead to anchor the TBM, and separate thrust cylinders press the rotating cutterhead against the tunnel face. The cutterhead rotates about a longitudinal axis such that the disc cutter assemblies roll along the face to fracture, loosen, grind, dislodge, and/or break materials from the tunnel face. The fractured and loosened material is collected and removed to gradually form the tunnel.
The disc cutter assemblies are typically removably retained between a pair of oppositely disposed housing halves (sometimes referred to as a housing assembly) that are fixedly attached to corresponding mounting plates on a TBM cutterhead assembly. The disc cutter assemblies are mounted such that the outer cutter ring extends from the face of the TBM cutterhead assembly to engage the tunnel face. Another illustrative tunnel boring machine is disclosed in U.S. Pat. No. 4,548,443, to Turner, and a main frame for a TBM is disclosed in U.S. Pat. No. RE 31511, to Spencer, which is hereby incorporated by reference.
In the partially exploded view in FIG. 1 a prior art disc cutter assembly 10 is shown between oppositely disposed mounting plates 19L, 19R that are typically permanently fixed to the TBM cutter wheel (not shown). Each mounting plate 19L, 19R supports a corresponding housing mount, also referred to as a housing half 20L, 20R. For example, the housing half 20L, 20R may be welded to the corresponding mounting plate 19L, 19R. In some embodiments the mounting plates 19L, 19R for all of the disc cutter assemblies 10 are permanently fixed to the cutter wheel, and a heat treatment is then applied to the cutter wheel assembly prior to attaching the housing halves 20L, 20R to the mounting plates 19L, 19R.
The disc cutter assembly 10 is mounted to the housing halves 20L, 20R, and includes an outer cutter ring 15 supported on a hub 12. The cutter ring 15 is positioned to engage the tunnel face during tunnel boring operations. Bearing assemblies (not shown) are provided between the shaft 13 and the hub 12 to provide for rotation of the hub 12 and cutter ring 15 about the shaft 13.
The housing halves 20L, 20R each define an L-shaped channel 21 having a long leg 21A and a short leg 21B. The L-shaped channel 21 is sized to slidably receive a shaped end of the cutter assembly shaft 13. The disc cutter assembly 10 is installed by inserting opposite ends of the shaft 13 into the long leg 21A of the channels 21 at the back of the housing mounts 20L, 20R. The disc cutter assembly 10 is slid along the long legs 21A of the L-shaped channel 21 and shifted laterally into the recess formed by the shorter legs 21B. The ends of the shaft 13 are secured to the housing halves 20L, 20R with wedge lock assemblies 22A that engage respective ends of the shaft 13.
The wedge lock assemblies 22A each include a wedge 22, a clamp block 24, and an optional tubular sleeve 28 disposed therebetween. The wedge 22 includes an angled face 22D that slidably engages an angled face 13D on the shaft 13, such that tightening the bolt 23 urges the shaft 13 end into the short leg 21B and against a seating surface of the housing half 20L, 20R. The clamp block 24 engages abutment surfaces 25 on the back end of the associated housing half 20L, 20R. The bolt 23 extends through the wedge 22, the sleeve 28, and the clamp block 24, and is secured with two nuts 26 and a washer 27. As the bolt 23 is tensioned by torqueing the nuts 26 to a design specification, the wedge 22 locks the cutter assembly 10 in place. The ends of the shaft 13 seat against faces 21C in the short legs 21B of the channel 21. It will be appreciated that the faces 21C (an in particular the face 21C facing downward in FIG. 1) must react the large and unsteady forces generated as the disc cutter assembly 10 cuts into the tunnel face.
The disc cutter assemblies 10 are subjected to very high forces during tunnel boring operations. Once excavation of the tunnel is started, it is difficult and time-consuming to repair or replace the disc cutter assemblies 10 because the assemblies are difficult to access in situ, and the cutter assemblies are heavy, often weighing many hundreds of pounds. Tunnels are often at significant depths, with correspondingly high ambient pressures. Therefore, it is critical that the installation of the cutter assembly in the cutterhead be very secure and reliable, even under the extreme conditions associated with tunnel boring.
In particular, the housing halves 20L, 20R are typically welded onto the mounting plates 19L, 19R, and are therefore challenging to remove and replace if they become damaged. If a housing half 20L, 20R becomes damaged during use, it typically must be replaced in situ, which is difficult and may shut down the TBM for an extended period of time.